GIS-Based Characteristic Analysis of Shoals Evolution Around Alluvial Islands in the Changjiang Estuary

Seven pieces of charts of the Changjiang estuary from 1879 to 2000 are digitized and digital elevation model (DEM) of the Changjiang estuary in different periods is established supported by GIS, based on which, the shoals around Changxing-Hengsha Island and Jiuduansha is visualized, the change of area, volume, the amount and thickness of erosion-accretion and horizontal transposition rate of depth contour are calculated. The results show that: the trend of the second and third generation of the shoals around alluvial islands in the Changjiang estuary in the past 150 years is that deposition is as a whole and progradation seaward along southeast with deposition rates is faster than that of previous time; there are a total of 1.948 billion tons of sediment from 1879 to 2000, with the average annual deposition of 16.1millin tons, nearly accounting for 3.72% of sediment flux in Datong, and with the average annual sediment thickness of 0.83 cm. The deposition rates differ in different periods, and some time there is even a certain degree of erosion; erosion-accretion status differs in different shoals, shoals of Changxing-Hengsha Island are in washed status, east of Hengsha Island and Jiuduansha are in siltation status; the natural evolution of shoals is an important part in the growth development of the Changjiang estuary and constrained by the amount of sediment in the Changjiang stream; with the increasing intensity of development in stream and the increasing number of coastal engineering in the estuary, the impact of human activities on the shoals around alluvial islands is becoming more and more intense, and the natural evolution process of shoals would even change.